A lot of people are wondering why Nokia didn't choose to go with Android. How can Nokia differentiate themselves when Android is a lot more open and free than Windows Phone 7? As usual, the key to this is in the details. If you read the announcements carefully, you'll see that Microsoft offered Nokia something Google most likely didn't. Update: What a surprise. Elop just confirmed Nokia has a special deal with Microsoft. Whereas HTC, Samsung, and so on are not allowed to customise WP7 - Nokia is, further confirming my theory.

No one who has bought an Android phone cares I'm afraid. Developers and users also don't want a third application store that has absolutely nothing in it. There's only so much you can do gaming-wise on a phone as well.

Besides, OEMs and operators have all said they want a third way.

They haven't. Microsoft claims that they have, but they just haven't. They have enough on their plate at the moment supporting iOS and Android as well as Symbian. You can't complain about fragmentation on the one hand and then claim that another OS is going to make any difference.

The market has made it abundantly clear that they don't want a Windows phone for a very, very long time. That's why the past few years are littered with companies who've got burned partnering with Microsoft on mobiles.

Windows Phone has failed. It's time to identify the reasons why and either do something about them or can the thing. Putting loaded CEOs into other companies to use your products that end up getting burned when you fail is not going to work.

Microsoft gets partners (aka cannon fodder) when those partners are in trouble. They get milked dry by MS and then left for dead.
MS have done this many times before. They get caught with their hands in the cookie jar, pay the cost in court (sometimes hundreds of millions) and walk away smiling sweetly to themselves.
They then integrate the stuff they have stolen/got caught/paid the fine for into their core products and then go on the prowl for the next sucker company to grind into the dust.
My guess is that Nokia will wither & die in 2-3 years. I'd love to be proved wrong and that MS has changed but there is far too much of a hint of 'desperation' in this move by Nokia to leave me with any confidence.